1. Field of the Invention
The present invention relates to nanoparticles. More particularly, the present invention relates to a method for transferring inorganic oxide nanoparticles from aqueous phase to organic phase.
2. Description of the Related Art
Organic/inorganic composites have been developing for decades. Comparing to the pure plastics, the performance of the organic/inorganic composites such as tensile strength, thermal deformation temperature and modulus has been improved remarkably. Thus, the organic/inorganic composites have become used widely in the application of improving physical properties.
At present, the existing flexible plastic substrate materials still fail to withstand the high-temperature conditions in the manufacturing process due to their poor thermal resistance and dimensional stability. In the applications of optoelectronic field, epoxy resins are usually used as packaging materials. However, the shortcoming of epoxy resins is having an incompatible coefficient of thermal expansion with the devices. When the resin is cooled after curing, the changes of temperature may lead to cracks or breakdown of the device. Thus, inorganic additives may be added into the resins to improve the physical properties.
Nanocomposites including organic/inorganic materials have been used widely in daily necessities, 3C electronics and plastic substrates of display. Furthermore, the combination of inorganic oxide nanoparticles with polymers to form polymer nanocomposites results in more excellent properties than the conventional composites, such as enhanced mechanical properties, better dimensional stability, better thermal stability and so on. Therefore, the polymer nanocomposites could be an answer for resolving the problems about the poor thermal resistance of optoelectronic packaging materials. However, there are still some problems needed to resolve. For example, the main problem needs to be resolved is how to combine the inorganic oxide nanoparticles with polymers without aggregations, such that novel polymer nanocomposites having high-performance and multi-function may be formed.
A method of phase transfer for directly transferring the inorganic oxide nanoparticles from aqueous phase to organic phase is an easy and rapid way to disperse the hydrophilic inorganic oxide nanoparticles in the organic solvent. U.S. Pat. No. 6,736,891 discloses a method of phase transfer for modifying the inorganic oxide particles by reacting with modifiers or surfactants that the surface polarity of the inorganic oxide particles may be changed from hydrophilic to hydrophobic. Therefore, the modified inorganic oxide particles can be transferred into the organic solvent. However, the size of inorganic oxide particles is micro-scaled even by wet-milling to reduce the particle size. The micro-scaled particles may not be dispersed uniformly when combined with the polymers, resulting in poor transparency due to light scattering.
In WO Patent Publication 2008/071248, various amphiphilic block copolymers are dissolved in non-polar solvent, combined with an aqueous dispersion of silica naoparticles and alcohol to provide a homogeneous phase. Thereafter, water is added to the mixed solution to separate organic phase and aqueous phase. The silica nanoparticles are transferred into the organic phase together with the amphiphilic block copolymers attached thereto. However, the method requires different amphiphilic block copolymers depending on the characteristics of inorganic oxides. Therefore, the method is very complicated to carry out, and the transferred nanoparticles containing about 30-40 wt % of organic component are not cost-effective.
In U.S. patent Publication 2004/147029, the organic dispersion of synthesized silica nanoparticles need huge amounts of water for diluting. Furthermore, the diluted solution needs huge amounts of high boiling point solvent for multiple distillation and phase transfer.
Therefore, in the field of polymer nanopcomposites, an important issue is to develop a simple and cost-effective method for transferring the inorganic oxide nanoparticles from aqueous to organic phase. Furthermore, the method can be used to form a polymer composite with uniformly dispersed nanoparticles therein by controlling the particle size of the nanoparticles and reducing the content of organic materials attached thereon.